1. Field of the Invention
The instant invention is directed to golf balls, and more particularly to a ball having the optimal cover composition, cover hardness, center weight, the size of the thread windings, and dimple configuration to provide superior playability capabilities with respect to softness and spin without sacrificing superior distance capabilities.
2. Description of the Related Art
There are a number of physical properties that affect the performance of a golf ball. The core of the golf ball is the source of the ball""s major elastic properties. Among other things, the core affects the ball""s xe2x80x9cfeelxe2x80x9d and its initial velocity. The initial velocity is the velocity at which the golf ball travels immediately following impact. The initial velocity can be grouped with launch angle and spin to describe the ball""s initial conditions, or the conditions exhibited by the ball immediately after impact. The initial conditions along with dimple pattern determine the ball""s trajectory and ultimately its distance. The xe2x80x9cfeelxe2x80x9d is the overall sensation transmitted to the golfer through the golf ball at impact. The overall construction of the ball influences the xe2x80x9cfeelxe2x80x9d of a golf ball. Properties such as cover hardness, compression, and rebound can be used to gauge the response of a golfer to a ball""s construction. But ultimately, the ball""s xe2x80x9cfeelxe2x80x9d can only be determined by the avid golfer. One property commonly tested by golfers to judge the xe2x80x9cfeelxe2x80x9d of a ball is the sound made at impact between the ball and the club. This sound or xe2x80x9cclickxe2x80x9d provides the golfer with a lasting impression of the ball""s feel. Generally, lower cover hardness, compression, and rebound give the golfer an impression of a softer xe2x80x9cfeelxe2x80x9d and a corresponding lower, softer click.
Until the late 1960""s, most golf balls were constructed with a thread wound core and a cover of compounds based on natural balata and gutta percha or synthetic transpolyisoprene. These golf balls have been and are still known to provide good flight distance. Additionally, due to the relative softness of the balata cover, skilled golfers can impart various spins on the ball in order to control the ball""s flight path (e.g., xe2x80x9cfadexe2x80x9d or xe2x80x9cdrawxe2x80x9d) and xe2x80x9cbitexe2x80x9d characteristics upon landing on a green.
xe2x80x9cFadexe2x80x9d is a term used in golf to describe a particular golf ball flight path that is characterized by a curved or arched flight exhibited towards the latter portion of the flight path that veers off from the center line of the initial flight path to the opposite side from which the golfer stands. Upon contact with the ground, a ball hit with a xe2x80x9cfadexe2x80x9d will stop in a relatively short distance. This is a result of an open club face at impact imparting more spin and a higher trajectory than normal.
xe2x80x9cDrawxe2x80x9d is the term used in golf to describe a particular golf ball flight path that is characterized by a curved or arched flight exhibited towards the latter portion of the flight path that veers off from the center line of the initial flight path to the same side on which the golfer stands. Upon contact with the ground, a ball hit with a xe2x80x9cdrawxe2x80x9d, unlike that of a ball hit with a xe2x80x9cfadexe2x80x9d, will roll for a considerable distance. This is a result of a closed club face at impact imparting less spin and a lower trajectory than normal.
xe2x80x9cCheckxe2x80x9d or xe2x80x9cbitexe2x80x9d is the term used in golf to describe the effect of imparting a substantial amount of backspin to an approach shot to a green that causes the golf ball to stop abruptly upon contact with the green.
Another desirable feature of balata-based compounds is that they are readily adaptable to molding. These compounds therefore can be easily compression molded about a spherical core to produce golf balls.
Though possessing many desirable properties, there are substantial drawbacks to use of balata or transpolyisoprene-based compounds for golf ball covers. From a manufacturing standpoint, balata-type materials are expensive and the manufacturing procedures used are time consuming and labor-intensive, thereby adding to the material expense. From a player""s perspective, golf balls constructed with balata-based covers are very susceptible to being cut from mishits and being sheared from sharp grooves on a club face. As a result, they have a relatively short life span.
In response to these drawbacks to balata-based golf ball covers, the golf ball manufacturing industry has shifted to the use of synthetic thermoplastic materials, most notably ionomers sold by E. I. DuPont De Nemours and Company under the name SURLYN(copyright). Surlyn is an ionomeric resin that is an ionic copolymer of an olefin having from about 2 to about 8 carbon atoms, such as ethylene, and a metal salt of an alpha, beta-ethylenically unsaturated mono- or dicarboxylic acid such as acrylic acid, methacrylic acid, or maleic acid. The pendent ionic groups in the ionomeric resins interact to form ion-rich aggregates contained in a non-polar polymer matrix. Metal ions, such as sodium, zinc, or lithium are used to neutralize some portions of the acid groups in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties such as improved durability.
Thread wound balls with ionomer covers are less costly to manufacture than balls with balata covers. They are more durable and produce satisfactory flight distance. However, these materials are relatively hard compared to balata and thus lack the xe2x80x9cfeelxe2x80x9d of a balata covered golf ball.
In an attempt to overcome the negative factors of the hard ionomer covers, DuPont introduced low modulus SURLYN(copyright) ionomers in the early 1980""s. These SURLYN(copyright) ionomers have a flexural modulus of from about 3000 to about 7000 PSI and hardness of from 25 to about 40 as measured on the Shore D scalexe2x80x94ASTM 2240. The low modulus ionomers are terpolymers, typically of ethylene, methacrylic acid and n or iso-butylacrylate, neutralized with sodium, zinc, magnesium or lithium cations. E.I. DuPont De Nemours and Company has disclosed that the low modulus ionomers can be blended with other grades of previously commercialized ionomers of high flexural modulus from about 30,000 to 55,000 PSI to produce balata-like properties. However, xe2x80x9csoftxe2x80x9d blends, typically 52 Shore D and lower (balata-like hardness), do not exhibit good physical properties and are prone to cut and shear damage.
The low modulus ionomers when used without blends produce covers with very similar physical properties to those of balata, including poor cut and shear resistance. Worse, wound balls with these covers tend to go xe2x80x9cout-of-roundxe2x80x9d quicker than wound balls with balata covers. Blending with hard SURLYN(copyright) ionomers was found to improve these properties.
Another approach taken to provide a golf ball cover that has the playing characteristics of balata is described in U.S. Pat. No. 5,334,673 (the ""673 patent) assigned to the Acushnet Company. The ""673 patent discloses a cover composition comprising a diisocyanate, a polyol and a slow-reacting polyamine curing agent. The diisocyanates claimed in the ""673 patent are relatively fast reacting. Due to this fact, catalysts are not needed to lower the activation energy threshold. However, since relatively fast-reacting prepolymer systems are used, the reaction rate cannot be easily controlled thereby requiring the implementation of substantial processing controls and precise reactant concentrations in order to obtain a desired product.
To avoid the problems associated with fast-reacting prepolymer systems, slow-reacting systems such as Toluene diisocyanate (TDI) prepolymer systems can be employed. However, these systems, while avoiding the problems associated with fast-reacting systems, present similar problems, albeit for different reasons. The most noteworthy problem with slow-reacting pre-polymer systems is the requirement for a catalyst.
By introducing a catalyst into the system, processing problems similar to those associated with fast-reacting pre-polymer systems are virtually inevitable. As is well known in the art, the use of a catalyst can severely restrict the ability to control the speed of the reaction, which is undesirable.
Historically, in addition to manipulating the cover composition of a golf ball, golf ball manufacturers have also varied the size and winding conditions of the thread windings layer as well as the weight of the center in three-piece golf balls in an effort to design a golf ball with superior ball performance. Various efforts have been made to select the optimal winding pattern as well as the ideal thread dimension and winding tension.
For many years golf ball manufacturers have also investigated changing dimple configurations in an effort to design a ball with superior distance capabilities. Dimples are the surface indentations or depressions on a golf ball. Specifically, many efforts have been made to select the optimum number, size and shape of dimples as well as their disposition around the outer surface of a generally spherically shaped golf ball.
As is well known in the art, ball manufacturers are bound by regulations of the United States Golf Association (USGA) which control many characteristics of the ball, including the size and weight of the ball, the initial velocity of the ball when tested under specified conditions, the overall distance the ball travels when hit under specified test conditions, and the ball""s aerodynamic symmetry. Under USGA regulations, the diameter of the ball cannot be less than 1.680 inches, the weight of the ball cannot be greater than 1.620 ounces avoirdupois, the initial velocity of the ball cannot be greater than 250 feet per second when tested under specified conditions (with a maximum tolerance of +2%), the driver distance cannot exceed 280 yards when tested under specified conditions (with a test tolerance of +6%), and the ball must perform the same aerodynamically, regardless of the orientation.
Accordingly, it is an object of the instant invention to optimize the combination of center weight, core compression, size and winding conditions of the thread layer, dimple configuration, cover composition, and cover hardness to provide a three-piece golf ball, which travels great distances, and at the same time complies with USGA regulations.
It is another object of the instant invention to provide a three-piece golf ball that has a soft xe2x80x9cfeelxe2x80x9d in combination with superior distance capabilities.
It is yet another object of the instant invention to provide a three-piece golf ball having a synthetic cover material that achieves the sound, feel, and playability and flight performance qualities of balata covered golf balls.
It is still a further object of the instant invention is to provide a three-piece golf ball having superior distance, trajectory and flight stability.
Another object of the instant invention is to provide a three-piece golf ball having a surface divided into a plurality of polygonal configurations or shapes for the location of dimples for enhancing the aerodynamic properties of the golf ball.
It is yet another object of the present invention to provide a golf ball cover composition that does not require a catalyst.
It is still a further object of the invention to provide a polyurethane formula that achieves hardness characteristics similar to those associated with balata without compromising the durability of the polyurethane material. In contrast, polyurethane systems such as those disclosed in the ""673 patent produce relatively high hardness ranges that obviate the possibility of providing a polyurethane system that can truly mimic the feel and playability of a balata-based product.
A further object of the present invention is to provide a golf ball cover material that has improved process manufacturing as well as improved durability and resilience over balata.
These and other objects of the instant invention will be apparent from a reading of the detailed description of the instant invention.
The invention achieves the above-described objectives by providing a three-piece golf ball having a heavy liquid-filled rubber center, a thread windings layer whose threads are a large gauge and which is wound to an xe2x80x9copenxe2x80x9d great circle pattern, a xe2x80x9csoftxe2x80x9d polyurethane cover, and a xe2x80x9crhombicosadodecahedronxe2x80x9d dimple pattern. The ball of the instant invention has a core compression in the range of 70 PGA to 100 PGA, a center weight in the range of 17-19 grams, an unstressed (not wound) thread dimension of about 0.024xc2x10.004 inches height by {fraction (1/16)}th of an inch width, a cover hardness in the range of about 46 Shore D to about 54 Shore D, and a dimple pattern based on the geometry of a rhombicosadodecahedron. This combination has been found to produce a ball with superior distance capabilities and superior playability capabilities with respect to softness and spin. The use of these properties in the golf ball of the instant invention is based on the recognition that it is the combination of the center weight, the size and pattern and tension of the thread windings, cover hardness, dimple configuration, dimple size and dimple shape that will produce a ball that will travel the greatest distance without compromising shot-making feel.
Table 1, below, provides an example of some test data on the performance of the ball of the invention versus a standard wound, balata, three-piece ball.
The golf ball of the present invention has a conventional, heavy, liquid-filled, spherical rubber center or rubber sphere that will be described in more detail in a later section. In a preferred embodiment of the invention, the center has a weight that is slightly heavier than in golf balls manufactured previously.
The thread of the golf ball of the invention is cut from a sheet that is about 0.020 inches to 0.028 inches in thickness or height. A typical thickness is 0.024 inches, which corresponds to a xe2x80x9cgaugexe2x80x9d of 24. The width of the thread cut for the instant invention is about {fraction (1/16)}th inch.
It has now been discovered that the combination of a relatively heavy center with a large gauge thread, of about 0.024xc2x10.004 inches, and having relatively low Swartz modulus, and width of about {fraction (1/16)}th of an inch (0.063xc2x10.004 inch), wound to promote an xe2x80x9copenxe2x80x9d winding pattern under a tension in the range of 700 to 950 grams of tension produces a ball with improvements in player characteristics. Typically, low Swartz modulus is in the range of 160 to 240 p.s.i., and in the preferred embodiment, between 180 to 220 p.s.i. Specifically, the heavy center surrounded by a thread windings layer comprised of a large gauge thread wound to a great circle winding pattern results in a three piece golf ball that spins less than known inventions when it is hit by a driver, while spinning more when it is hit by a pitching wedge. Lower spin off the driver is preferable as it increases the total distance attained from a golf ball.
The use of the relatively large gauge, wide thread, wound to an xe2x80x9copenxe2x80x9d winding pattern, allows the urethane polymer mixture into which the thread-wound liquid center is placed, to penetrate or seep into the thread windings layer to a greater extent than in the prior art balls. The result is a softer-feeling ball than would be attained otherwise.
It has been discovered that a blend of diamine curing agents with slow-reacting prepolymer systems eliminates the problems associated with catalysts while maintaining the advantages associated with slow-reacting prepolymer systems.
Polyurethane compositions comprising the reaction of polyurethane prepolymer and a curing agent are disclosed. The prepolymer comprises a diisocyanate such as Toluene diisocyanate (TDI) and a polyol such as polytetramethylene ether glycol (PTMEG). The curing agent is a blend of a slow-reacting diamine such as dimethylthio 2,4-toluenediamine with a fast-reacting diamine such as diethyl 2,4-toluenediamine, said mixture comprising about 1% to 20% by weight of dimethylthio-2,4-toluenediamine and the balance diethyl-2,4-toluenediamine.
In a preferred embodiment, TDI prepolymer having a low free isocyanate content (low free TDI) is used to reduce adverse effects that can arise from exposure to unreacted isocyanate. The curing agent blend provides flexibility to the formulation by eliminating the need for a catalyst.
As mentioned previously, in addition to manipulating the center and cover parameters in a golf ball, superior aerodynamic properties are also attributed to the dimple configuration on a golf ball. In the instant invention, the dimples are arranged on the surface of the golf ball based on the geometry of a rhombicosadodecahedron. This configuration is achieved by dividing the outer spherical surface of a golf ball into a plurality of polygonal configurations, including pentagons, squares and triangles for locating a plurality of dimples on the outer surface of the golf ball. The polygonal configurations of this invention are preferably a combination of regular pentagons, squares and triangles to cover the outer surface. This first plurality of polygonal configurations is generally referred to herein as a xe2x80x9crhombicosadodecahedronxe2x80x9d. The rhombicosadodecahedron is further characterized by a uniform pattern of pentagons formed over the outer surface each bounded by triangles and squares.
A pair of first polygonal configurations, each located on opposite sides of the outer surface, include one of the two poles symmetrically arranged within its boundaries. The outer surface has a plurality of dimples of different sizes. In one embodiment, the dimples are of first, second and third sizes and are generally located to have a first pattern associated with the pentagons, a second pattern associated with the squares, and a third pattern associated with the triangles. Dimples are preferably circular in shape, but can have a non-circular shape within the scope of this invention.
The combination of the aforementioned center, cover, thread windings layer, and dimple specifications produces a golf ball that possesses noticeable improvements in playability with regard to spin and feel while simultaneously being capable of being driven a long distance. The following table, table 2, shows test data results on spin related to thread size.
The liquid center, the cover (55 Shore D polyurethane), and the winding pattern (Great circle) being the same in the following groups, the spin off the 9.5xc2x0 driver at a ball velocity of 230 feet per second is as shown in Table 2.